1. Field of the Invention
The present invention relates to an over-current protection apparatus and the method for forming the same, and more particularly, to a three-dimensional over-current protection apparatus applied to a secondary battery and automotive application, and method for forming the same.
2. Description of Related Art
FIG. 1 depicts a cross-sectional view of a conventional over-current protection apparatus 10, comprising a first electrode 12, a second electrode 13 and a current-sensitive element 11. Usually, a first conductive metal termination 14 and a second conductive metal termination 15 are respectively adhered to the first electrode 12 and the second electrode 13 on the surfaces for electrically connecting to the cathode and anode of the secondary battery.
Nowadays, the common current-sensitive element 11 is composed of a conductive material having Positive Temperature Coefficient (PTC material). The resistance of the PTC conductive material can be kept extremely low at normal operation due to its low sensitivity to temperature variance so that the circuit can operate normally. However, if the over-current or over-temperature effect occurs, the resistance will immediately be increased to a high resistance state (e.g. above 104 ohm.) Therefore, the over current will be reversely eliminated and the objective to protect the circuit device can be achieved.
Generally, the normal resistance value of the current-sensitive element 11 is followed the conventional formula:
R=xcfx81xc3x97l/A,
in which xcfx81 is the conductive coefficient, l is the length and A is the area. Since the volume of the portable electronic products is becoming smaller and smaller, the space for the over-current protection apparatus also needs to be reduced comparatively. Therefore, according to the above formula, the normal resistance of the over-current protection apparatus will be increased.
Since the size of the secondary battery tends to become smaller, the confined space inside the secondary battery and the available space for installation of PTC will also become less. Therefore, it is necessary to provide a solution to improve the space efficiency of the secondary battery.
A major object of the present invention is to provide an over-current protection apparatus, wherein the shape of the apparatus can be varied according to the available space of the secondary battery to achieve the maximum space efficiency and conform to the requirement of the secondary battery being light, thin and small on the market.
A second objective of the present invention is to provide an over-current protection apparatus, wherein the shape of the apparatus is a three-dimensional structure, not like a two-dimensional structure of the conventional over-current protection apparatus, so as to increase the area of the current-sensitive element and reduce its normal resistance.
A third objective of the present invention is to provide an over-current protection apparatus, wherein the position of the conductive metal termination connected to the electrode can be changed according to the space requirement of the secondary battery so as to achieve the best space efficiency.
In order to achieve the above objectives and to avoid the disadvantages of the prior art, the present invention discloses an over-current protection apparatus, comprising a current-sensitive element, a first electrode and a second electrode. The present invention is characterized in that the over-current protection apparatus is a three-dimensional multi-layer bending structure formed by a bending process, which is different from the conventional over-current protection apparatus. The over-current protection apparatus of the present invention can be processed by heating, pressing, etching, cutting and multi-stage deformation and the like to prevent it from breakage during the bending process. Therefore, an over-current protection apparatus with at least one bending structure is formed. Moreover, the bending structure of the over-current protection apparatus of the present invention can be varied according to its located space so that the occupied space of the over-current protection apparatus is reduced. Furthermore, the effective area of the current-sensitive element is increased because of the bending structure of the over-current protection apparatus, so that the normal resistance value is also reduced.
The foregoing and other objectives and advantages of the invention and the manner in which the same are accomplished will become clearer based on the following detailed description taken in conjunction with the accompanying drawings.